Gas Gas SM 125 (2002-2010) Review: The Two-Stroke Supermoto That Refuses to Compromise

Introduction

When Gas Gas unleashed the SM 125 in 2002, they weren't just building a motorcycle – they were crafting a statement. This Spanish-made supermoto defied the norms of its era, packing race-bred DNA into a street-legal 125cc package. Nearly two decades later, swinging a leg over this lightweight riot machine still feels like uncorking a bottle of pure adrenaline. Let's dissect why this two-stroke remains a cult favorite among riders who value raw excitement over practicality.

Design & First Impressions

The SM 125's visual language screams purpose. With its angular Deltabox frame exposed like mechanical jewelry and that comically short wheelbase (1,475 mm/58.1 in), it looks ready to pivot on a dime. The 940 mm (37 in) seat height might intimidate shorter riders, but that's the price of admission for 340 mm (13.4 in) of ground clearance. Every component feels deliberately minimalist – from the kickstart lever (no electrics here) to the analog dash that keeps distractions to a minimum.

Engine Performance: Two-Stroke Theatre

At its heart lies a 124cc liquid-cooled two-stroke that's anything but polite. The Keihin PWK carburetor feeds this single-cylinder beast, producing 36.8 hp at 10,000 rpm – numbers that shame modern four-stroke 125s. Torque peaks at 25 Nm (18.6 lb-ft), but these figures only tell half the story.

Twist the throttle and the powerband hits like a switchblade. Below 7,000 rpm, it's docile enough for parking lot maneuvers. Cross that threshold and the front wheel starts writing checks the suspension struggles to cash. The 6-speed gearbox (with surprisingly tall ratios) demands constant interaction, turning every straightaway into a mechanical chess match. Fuel economy? Let's just say you'll become best friends with petrol stations – the 9.5L (2.5 gal) tank empties quicker than your courage reserves.

Chassis & Handling: Surgical Precision

The Deltabox frame – a mix of cromoly steel and aluminum swingarm – creates a chassis taut enough to telegraph road textures through the handlebars. Combine this with the Marzocchi 45mm upside-down forks (295mm/11.6in travel) and Öhlins rear shock (320mm/12.6in travel), and you've got suspension that laughs at urban potholes while remaining composed during aggressive cornering.

At 95 kg (209 lbs) dry, the SM 125 disappears beneath you mid-corner. The 17" wheels (120/60 front, 150/60 rear) offer tenacious grip, letting you exploit every millimeter of tire edge. Braking is handled by single discs (260mm front/220mm rear) – adequate for the weight, though serious canyon carvers might crave more initial bite.

Urban Warfare vs. Backroad Banditry

In city traffic, the SM 125 is both king and court jester. Filtering through gridlock becomes a video game, the narrow profile slipping through gaps that leave larger bikes stranded. The light clutch pull (hydraulic actuation helps) prevents hand cramps during stoplight marathons.

But unleash it on twisting backroads and the true magic happens. The riding position – upright and commanding – gives perfect control for flicking between hairpins. That explosive powerband keeps you dancing on the gearshift, each upshift timed to stay in the meat of the power curve. It's exhausting in the best possible way – a motorcycle that demands 100% engagement 100% of the time.

Competition: How It Stacks Up

In the 125cc supermoto arena, the SM 125 faced formidable rivals:

1. Aprilia SX 125:
   The Italian alternative offered similar power but with Rotax-engine reliability. However, Aprilia's chassis felt heavier (108 kg dry) and less playful at low speeds.

2. Husqvarna SMS 125:
   Sharing the same aggressive DNA, the Husky matched the Gas Gas on suspension components but suffered from tighter service intervals. Its six-speed box had closer ratios better suited to tight circuits.

3. Japanese 125cc Four-Strokes:
   Models like the Yamaha WR125X offered modern conveniences (fuel injection, electric start) but couldn't match the SM 125's power-to-weight ratio (36.8 hp vs 15 hp).

Where the Gas Gas excelled was in delivering big-bike dynamics in a small package. The premium Öhlins/Marzocchi suspension combo gave it an edge over rivals still using basic components, while the aggressive ergonomics appealed to riders transitioning from motocross.

Maintenance: Keeping the Beast Alive

Owning a two-stroke supermoto isn't a hobby – it's a relationship. Here's your survival guide:

Engine Care
- Top-End Rebuilds: Expect piston replacements every 50-60 hours of hard riding. MOTOPARTS.store offers Vertex piston kits that improve durability over stock components.
- Carb Tuning: The Keihin PWK responds well to jetting kits (available in our store) – crucial for altitude changes or aftermarket exhausts.
- Cooling System: Flush coolant annually and consider upgrading to high-performance radiator caps for better heat management.

Suspension Tuning
The Öhlins shock benefits enormously from regular nitrogen recharge (every 100 hours). Our selection of progressive-rate springs can tailor the ride for street vs. track use.

Brake Upgrades
While the stock brakes suffice for most riders, MOTOPARTS.store carries sintered pads that improve bite and reduce fade during aggressive use.

Two-Stroke Essentials
- Always use synthetic premix oil (we recommend Motul 710 at 40:1)
- Clean power valve every 30 hours using our specialized cleaning kits
- Replace spark plugs every 20 hours – NGK BR9EG works best for modified engines

The Modern Legacy

In an era dominated by four-strokes and emission regulations, the SM 125 stands as a glorious anachronism. It's not about nostalgia – this machine remains relevant through pure, undiluted performance. The lack of rider aids forces skill development, making it a favorite for advanced riders looking to hone their craft.

While newer models offer push-button starts and fuel injection, they can't replicate the SM 125's visceral thrill. That manic scream as the powerband hits, the way it flicks between corners like a hyperactive ferret – these are experiences modern electronics can't sanitize.

Conclusion: Who Should Consider One Today?

The Gas Gas SM 125 isn't for everyone. It demands mechanical sympathy, rewards skilled inputs, and punishes complacency. But for riders willing to embrace its quirks, it offers an authenticity that's become rare in modern motorcycling. Whether you're hunting for a weekend toy or the ultimate urban escape vehicle, this Spanish firecracker delivers grins per euro like few others.

At MOTOPARTS.store, we keep these legends alive with a comprehensive range of performance parts and OEM replacements. From upgraded expansion chambers to modern radial brake upgrades, we've got everything to make your SM 125 sharper than ever. After all, legends deserve immortality.

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Specifications sheet

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